This year, the poaching of over 430 rhinos in South Africa has rightly dominated the news. The massacre of these animals has forced the government to respond with more rangers in Kruger national park and stronger surveillance in the airports. Sadly, the energy and hand-wringing to protect one species is not extending to another. South Africa's lions are down to the last few prides, with just 2,000 living in the wild. But the failure to curb the nascent but burgeoning trade in lion bones could see this drop even further.

According to CITES, between 2009 and 2010 exports of lion bones from South Africa have risen by 250%. Hundreds of thousands of people have called on the government to act to save these majestic creatures. The reaction so far: stubborn denials and political censorship to silence the growing drumbeat of lion campaigners.

Dr Pieter Kat, a trustee of LionAid, says that by creating a supply for the trade in lion bones, South Africa has created growing levels of lion poaching across Africa, fuelled in large part by the much higher premium paid in East Asia for wild lion bone over its farmed alternative. But environment minister Edna Molewa has refused to acknowledge this risk, slapping a target on the forehead of the last remaining lions. The statistics are alarming. In the last 40 years, the African lion population has plummeted from roughly 200,000 to around 20,000 today.

More than 700,000 people, many of them in South Africa, have backed a campaign by the online campaign organisation Avaaz calling on President Zuma to save Africa's last lions. Rather than allow the debate to flow, however, it has been gagged. When ads asking Zuma to take action went up in the Johannesburg airport next to the baggage carousel, they were torn down by the airports authority.

The adverts – which were being seen by tens of thousands flying into the city – were powerful but not insulting: a picture of Zuma looks on as a lioness stares down the barrel of a gun, with the caption reading: "Our lions are being slaughtered to make bogus sex potions for Asia. Will President Zuma save them? Urge him to stop the deadly lion bone trade now."

These adverts break no law and are a protected form of free expression under the South African constitution. As this campaign to save the lions in South Africa has been censored by the government-owned airport authority, Avaaz has launched legal proceedings against Airports Company South Africa (Acsa) and its advertising firm Primedia (which had approved the ads before their hanging). Acsa announced this week it planned to dig in its heels and defend its political censorship.

South Africa is committed to conservation and it has forcefully protected at-risk species from poachers in the past, including taking swift action to save the rhino. But failing to act on lions exposes a conservation policy that can seemingly only cope with one burning issue at a time.

The first step to solving this problem is for the government to first admit that there is a problem. This is not confined to canned lions – where animals are kept in a confined area to facilitate the hunt – but threatens a dangerous escalation in illegal poaching. Zuma has the power right now to institute a ban. Prohibitive sentences for commercial poachers and enhanced monitoring of airports and harbours to reduce the flow of these products would go a long way towards stemming the proliferation in illegal poaching. Effective laws must be put in place to cut off any legal loopholes and extinguish this shameful trade before one of the world's most majestic and celebrated creatures is relegated to a greed-fuelled and needless demise.